(a)[3]
The sample showed that 102 adults travel by bus. Find an approximate $90\%$ confidence interval for the proportion of all the adults in Fromleigh who travel by bus.
(b)[3]
The survey included a question about the amount, $x$ dollars, spent on travel per year. The results are summarised as follows: $n = 250$, $\sum x = 50460$, $\sum x^2 = 19\,854\,200$. Find unbiased estimates of the population mean and variance of the amount spent per year on travel.
(c)[1]
A councillor wanted to select a random sample of houses in Fromleigh. He planned to choose the first house on each of the 143 streets in Fromleigh. Explain why this would not give a random sample.